1. Field of the Invention
This invention relates to belt-like bag bodies, and more particularly to an improvement of a belt-like bag body for use in a silt fence, an oil fence, a rubber dam, a hydraulic jack, a sink-float type fishpond and the like.
2. Related Art Statement
As this type of the bag body, there is a belt-like bag body as shown in FIGS. 7 and 8. This bag body 1 comprises a belt-like rubber sheet 2 and a non-adhesion region 3 located in a central portion in the thickness direction of the rubber sheet 2 so as to extend toward the widthwise direction thereof and capable of separating the rubber sheet 2 to upper sheet portion 2a and lower sheet portion 2b for forming a gas or liquid passage. Furthermore, the belt-like bag body 1 is provided with a layer-like reinforcing canvas 5 located outside the rubber sheet 2 and surrounding this rubber sheet 2. Moreover, the bag body 1 comprises an outer coating rubber 7 covering the outer surface of the reinforcing canvas 5, if necessary. This coating rubber 7 is provided with two reinforcing canvases 6 located in the upper and lower portions of the bag body 1 in parallel to each other for reinforcing the reinforcing canvas 5.
In use of this belt-like bag body 1, water, air or other fluid is supplied to the non-adhesion region 3 in the rubber sheet 2 to largely separate the central portion of the rubber sheet 2 and expand it into a substantially circular form as shown in FIG. 8. A fluid passage 8 is thus formed for use in the silt fence, oil fence or the like.
In the conventional belt-like bag body, however, a large stress concentration occurs in the rubber sheet 2 at a widthwise end 3a of the non-adhesion region 3 between the reinforcing canvas 5 and the passage 8 during the expansion of the rubber sheet 2, and consequently cracks 9 are created in the rubber sheet 2. When the bag body 1 is used over a long time, the crack 9 grows to arrive at the reinforcing canvas 5. In the latter case, the fluid in the passage 8 arrives at the reinforcing canvas 5 through the crack 9. Furthermore, the fluid leaks up to the outer reinforcing canvas 6 along the fibers constituting the canvas 5 to finally cause swelling trouble, puncture and the like.